High molecular weight linear polyesters and polymers of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et al, U.S. Pat. No. 3,047,539. These patents disclose that the polyesters are particularly advantageous as film and fiber-formers.
Poly(1,4-butylene terephthalate), because of its very rapid crystallization from melt, is uniquely useful as a component in such compositions. Work pieces molded from these polyester resins, in comparison with other thermoplastics, offer a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction.
One useful family of such compositions comprises those which are reinforced, e.g., with from about 5 to about 55% filamentous glass, based on the weight of glass and polyester components, and rendered flame retardant by the incorporation of a flame-retarding amount of a flame-retarding component. Another useful family of such compositions comprises those containing poly(1,4-butylene terephthalate), a flame retardant and, optionally, a reinforcing agent and a polycarbonate resin.
Experience has shown, however, that typically, articles molded from these afore-described polyester compositions are characterized by poor notched Izod impact strength. U.S. Pat. No. 4,080,354, Kramer, disclose styrene-propylene-butadiene impact modifiers for poly(1,4-butylene terephthalate) resins. U.S. Pat. No. 4,096,202, Farnham, et al, disclose core-shell impact modifiers for, among other resins, poly(1,4-butylene terephthalate) resins. Core-shell impact modifiers have become widely used in thermoplastic resins, particularly glass reinforced resins, to increase Izod impact strength. However, even though such glass reinforced, impact modified, thermoplastic resins show improved Izod impact strength, they are still rather poor in notched Izod impact strenth.
It has now been surprisingly discovered that the incorporation of cuprous iodide unexpectedly improves the impact strength of flame retarded, glass reinforced, impact modified, poly(1,4-butylene terephthalate) resin molding compositions.